Name: covalent bond overlap and orbital hybridization
Uploaded: 2025-05-22T09:05:33.000Z
Duration: 2 min 38 s
Channel: JoVE

La teoria del legame di valenza propone che un legame chimico risulti da una sovrapposizione di orbitali atomici parzialmente riempiti, compresi quelli diversi dall'orbitale sferico s.
Quando si forma un singolo legame tra due orbitali non sferici, i due orbitali avranno una sovrapposizione testa a testa.
Il tipo di legame covalente formato dalla sovrapposizione testa a testa degli orbitali atomici è chiamato legame sigma.
Gli orbitali s e p che si sovrappongono per formare legami covalenti non possono produrre le varie forme molecolari nel modello VSEPR. La teoria del legame di valenza aiuta a spiegare questa geometria molecolare attraverso l'ibridazione, o mescolamento, degli orbitali atomici.
Alcuni orbitali atomici coinvolti nel legame si ricombinano per formare nuovi orbitali le cui forme sono un ibrido degli originali. Il numero iniziale di orbitali atomici e il numero di orbitali ibridi generati è sempre lo stesso.
Gli orbitali ibridi hanno una forma diversa dai loro orbitali atomici costituenti, con un lobo che è significativamente più grande dell'altro. Pertanto, la densità di probabilità elettronica è altamente concentrata in un lobo direzionale, il che porta a una sovrapposizione più efficace con gli orbitali di altri atomi. Per chiarezza, questi orbitali sono spesso mostrati senza i lobi minori.
Ad esempio, nello stato eccitato del carbonio, l'uno s e i tre orbitali p che contengono i quattro elettroni spaiati subiscono ibridazione, producendo quattro orbitali ibridi s-p-tre equivalenti che occupano i vertici di un tetraedro regolare.
La miscelazione di un orbitale s e due orbitali p nello stato eccitato del carbonio genera tre orbitali ibridi equivalenti s-p-two con geometria planare trigonale.
Allo stesso modo, l'ibridazione di un orbitale s e uno p può creare due orbitali sp orientati a 180 gradi l'uno rispetto all'altro. 
Il concetto di ibridazione fornisce anche una spiegazione per la formazione di legami multipli. La sovrapposizione laterale di due orbitali p dà origine a un legame pi greco.
Tuttavia, un legame pi greco può essere formato solo in doppi e tripli legami quando esiste già un legame sigma tra due atomi. Poiché il legame pi greco esiste sui lati opposti dell'asse internucleare, i legami pi greco non sono in grado di ruotare attorno a questo asse.

teoria del legame di valenza e orbitali ibridi

Valence Bond Theory and Hybridized Orbitals

Secondo la teoria del legame di valenza, un legame covalente risulta quando: (1) un orbitale su un atomo si sovrappone ad un orbitale su un secondo atomo e (2) i singoli elettroni in ciascun orbitale si combinano per formare una coppia di elettroni. La forza di un legame covalente dipende dal grado di sovrapposizione degli orbitali coinvolti. La massima sovrapposizione è possibile quando gli orbitali si sovrappongono su una linea diretta tra i due nuclei.

Un legame σ (legame singolo in una struttura di Lewis) è un legame covalente in cui la densità elettronica è concentrata nella regione lungo l'asse internucleare. Un legame π è un legame covalente che risulta dalla sovrapposizione affiancata di due orbitali p. In un legame π, le regioni di sovrapposizione orbitale si trovano sui lati opposti dell'asse internucleare, mentre lungo l'asse è presente un nodo (un piano senza probabilità di trovare un elettrone). Tutti i legami singoli sono legami σ, mentre i legami multipli sono costituiti sia da legami σ che da legami π.

Quando gli atomi sono legati insieme in una molecola, le funzioni d'onda degli orbitali atomici possono combinarsi tra loro per produrre nuove descrizioni matematiche che hanno forme diverse. Questo processo è chiamato ibridazione ed è matematicamente realizzato dalla combinazione lineare degli orbitali atomici. I nuovi orbitali risultanti sono chiamati orbitali ibridi.

Le forme e gli orientamenti degli orbitali ibridi, che si formano solo in atomi con legami covalenti, sono diversi da quelli degli orbitali atomici in atomi isolati. Il numero di orbitali ibridi è uguale al numero di orbitali atomici che sono stati combinati per generarli. Tutti gli orbitali in un insieme di orbitali ibridi sono equivalenti in forma ed energia e il loro orientamento è previsto dalla teoria VSEPR. Gli orbitali ibridi si sovrappongono per formare legami σ, mentre gli orbitali non ibridati si sovrappongono per formare legami π.

Ad esempio, nello stato eccitato del carbonio, l’orbitale 2s e i tre orbitali 2p subiscono ibridazione producendo quattro orbitali ibridi sp3 degeneri tetraedrici. In una molecola di metano, l'orbitale 1s di ciascuno dei quattro atomi di idrogeno si sovrappone ad uno dei quattro orbitali sp3 dell'atomo di carbonio per formare un legame sigma (σ).

Allo stesso modo, la sovrapposizione di un orbitale 2s e due orbitali 2p del carbonio genera tre orbitali ibridi sp2 equivalenti con geometria planare trigonale, mentre l'ibridazione di un orbitale 2s e uno degli orbitali 2p crea due orbitali sp orientati a 180° l'uno rispetto all'altro.

Per gli atomi che hanno orbitali d nei loro sottolivelli di valenza, l'ibridazione di cinque orbitali atomici del guscio di valenza (uno s, tre p e uno degli orbitali d) genera cinque orbitali ibridi sp3d con geometria bipiramidale trigonale. Una disposizione ottaedrica di sei orbitali ibridi si ottiene sovrapponendo sei orbitali atomici del guscio di valenza (un s, tre p e due orbitali d), che produce sei orbitali ibridi sp3d2.

Questo testo è stato adattato da <a href="https://openstax.org/books/chemistry-2e/pages/8-1-valence-bond-theory">Openstax, Chemistry 2e, Section 8.1 Valence Bond Theory</a> and <a href="https://openstax.org/books/chemistry-2e/pages/8-2-hybrid-atomic-orbitals">Section 8.2 Hybrid Atomic Orbitals</a>.

Teoria del legame di valenza e orbitali ibridi

Secondo la teoria del legame di valenza, un legame covalente risulta quando: (1) un orbitale su un atomo si sovrappone a un orbitale su un secondo atomo, e (2) il singolo ...

valence-bond-theory-and-hybridized-orbitals

Education

Didattica

JoVE Core

Organic Chemistry

Chimica Organica

Unit 1

Unità 1

Covalent Bonding and Structure

Legame covalente e struttura

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

covalent bond overlap and orbital hybridization

Covalent bonds form when orbitals on two atoms overlap and their single electrons pair up. The bond is stronger when the overlap is greater. Maximum overlap happens when the orbitals meet along a direct line between the two nuclei.

A sigma bond, or σ bond, is the kind of covalent bond found in a single bond in a Lewis structure. In a σ bond, electron density is concentrated along the internuclear axis. A pi bond, or π bond, forms when two p orbitals overlap side by side. In a π bond, the overlap lies on opposite sides of the internuclear axis, and a node with no electron probability lies along the axis. Single bonds are σ bonds, while multiple bonds include both σ and π bonds.

When atoms join in a molecule, atomic orbital wave functions can combine to make new orbital shapes. This process is called hybridization, and it is described by the linear combination of atomic orbitals. The new orbitals are called hybrid orbitals. They form only in covalently bonded atoms, and their shapes and orientations differ from those of atomic orbitals in isolated atoms. The number of hybrid orbitals matches the number of atomic orbitals used to make them. Orbitals in one hybrid set have the same shape and energy, and their directions follow VSEPR theory. Hybrid orbitals form σ bonds, while unhybridized orbitals form π bonds.

Carbon shows this pattern clearly. In its excited state, one 2s orbital and three 2p orbitals hybridize to form four equivalent sp3 orbitals arranged tetrahedrally. In methane, each hydrogen 1s orbital overlaps with one carbon sp3 orbital to make a σ bond. One 2s orbital and two 2p orbitals can also mix to make three equivalent sp2 orbitals with trigonal planar geometry. When one 2s orbital mixes with one 2p orbital, two sp orbitals form and point 180° apart.

Atoms with d orbitals in the valence shell can form larger hybrid sets. Mixing five valence shell atomic orbitals, one s, three p, and one d, gives five sp3d hybrid orbitals with trigonal bipyramidal geometry. Mixing six valence shell atomic orbitals, one s, three p, and two d, gives six sp3d2 hybrid orbitals with octahedral geometry.

Covalent Bond Overlap and Orbital Hybridization

covalent-bond-overlap-and-orbital-hybridization

what is organic chemistry?

Carbon Compounds in Everyday Life

Organic chemistry focuses on carbon compounds called organic compounds. These compounds may come from living things or be made by chemists. Carbon is the main element in them, and it bonds with other carbon atoms as well as hydrogen, oxygen, nitrogen, and sulfur. Carbon can form up to four strong bonds. That ability lets carbon atoms build chains and rings of many sizes, shapes, and levels of complexity. Not every carbon-containing substance is classified as organic. Carbonates, cyanides, and...

electronic structure of atoms

Atomic Orbitals and Quantum Numbers

Atomic orbitals and quantum numbers describe how electrons are arranged around the nucleus. An atom has a small, positively charged nucleus with electrons surrounding it. The nucleus contains protons and neutrons, and the quantum mechanical model gives a better picture of this structure than older models. Protons carry a +1 charge and have a mass of 1.0073 amu. Neutrons have no charge and have a mass of 1.0087 amu. Electrons carry a −1 charge and have a mass of 0.00055 amu. The number of...

electron configurations

How Electrons Fill Atomic Orbitals

Electron filling in atoms follows a set order based on orbital energy. The Aufbau principle says each new electron enters the lowest-energy subshell available. The Pauli exclusion principle says no two electrons can share the same set of four quantum numbers. Hund’s rule of maximum multiplicity says electrons stay unpaired in equal-energy orbitals when possible. The order of filling follows the relative energies of the subshells. A common sequence is 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, and so on.

chemical bonds

Chemical Bonds: Types and Strength

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polar covalent bonds

Electronegativity in Polar Covalent Bonds

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lewis structures and formal charges

Lewis Structures, Bonds, and Formal Charge

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vsepr theory

Molecular Shapes from Electron Pairs

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molecular geometry and dipole moments

Predicting Shape and Molecular Polarity

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Resonance in Nitrite and Carbonate Ions

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valence bond theory and hybridized orbitals

Covalent bonds form when orbitals on two atoms overlap and their single electrons pair up. The bond is stronger when the overlap is greater. Maximum overlap happens when the orbitals meet along a direct line between the two nuclei. A sigma bond, or σ bond, is the kind of covalent bond found in a single bond in a Lewis structure. In a σ bond, electron density is concentrated along the internuclear axis. A pi bond, or π bond, forms when two p orbitals overlap side by side. In a π bond, the...

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Bond Order and Molecular Orbitals

Molecular orbital theory explains how electrons are arranged in molecules. It treats electron regions in a molecule much like atomic orbitals in an atom. A molecular orbital is the region of space where a valence electron is most likely to be found. Molecular orbitals form through the linear combination of atomic orbitals, or LCAO. When atomic wave functions combine in phase, they create regions with high electron density. When they combine out of phase, they create nodes, or regions with no...

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introduction to functional groups

Functional Groups and Organic Molecules

Functional groups are groups of atoms with specific chemical properties that appear within organic molecules. They are sometimes shown as "R." These groups sit along the carbon backbone of macromolecules, which can form chains or rings of carbon atoms. Functional groups help functionalize a compound. That means they can give the molecule different physical and chemical properties. In organic chemistry, this change in group structure can strongly affect how a compound behaves. Common...

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Advanced Functional Groups in Organic Chemistry

Advanced functional groups are atom clusters in organic molecules that give those molecules specific chemical properties. They are sometimes shown as "R" in formulas. By changing the atoms attached to a carbon skeleton, a functional group can make a compound behave differently in physical and chemical reactions. This topic covers several major classes of organic compounds with advanced functional groups. Aromatic hydrocarbons include benzene. Phenol is another example and is also called...

key terms and concepts

Learn how orbital overlap forms sigma and pi bonds, then see how hybridization creates sp3, sp2, sp, sp3d, and sp3d2 orbitals in molecules.

Covalent Bond Overlap and Orbital Hybridization | JoVE K12

organic chemistry

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Covalent Bond Overlap and Orbital Hybridization

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